1. Field of the Invention
The present invention relates to cranes, and, more particularly, to heavy duty cranes for lifting heavy loads.
A conventional crane has a lower works, and an upper works which is mounted, through a turntable bearing, for rotation on the lower works. A boom is pivotally connected to one end of the upper works, and a counterweight is secured to the other end of the upper works. In this type of crane, the weight of the load, and the weight of the counterweight, must be transmitted to the lower works (and the ground) through the turntable bearing. Consequently, the load which can be lifted by the crane is limited to a load which can be supported by the upper works without damage to the turntable bearing, and/or without exceeding a safe margin on overturning.
2. Description of the Prior Art
Many efforts have been made in the past to transfer the load carried by the boom, and/or the weight of the counterweight, around (instead of through) the turntable bearing.
The United States patent to Holt No. 1,159,841 shows an upper works (or swing frame) rotatably mounted on a lower works (or main frame). A boom is mounted at one end of the upper works, and a heavy prime mover (which acts to counterbalance the load) is mounted at the other end of the upper works. A pair of slide blocks is mounted under the prime mover, between the upper works and the lower works to partially support the load imposed on the upper works and transfer that load to the lower works.
The United States patent to Scheuerpflug No. 2,910,189 shows an upper works mounted for rotation on a lower works. A boom is pivotally mounted on an intermediate member which, in turn, is pivotally connected to the upper works. The intermediate member rolls on a way on the lower works to transmit the load of the boom directly to the lower works (and around the upper works).
The Netherlands Pat. No. 6,405,689 shows an upper works mounted on a lower works wherein the boom is mounted on a separate wheeled vehicle for transmission of the load directly to the ground.
The United States patent to Beduhn No. 3,485,383 shows a crane with an upper works mounted for rotation on a lower works. An auxiliary support ring mounted on the ground surrounds the lower works, and supports one end of a carrier which is pivotally connected to the upper works. A boom is mounted on the end of the carrier supported by the ring to transfer the load of the boom through the support ring to the ground. The machine has two counterweights, one permanently mounted on the upper works and one slidably mounted on the upper works but supported by the support ring.